The wireless local-area network (WLAN) technology known as “Wi-Fi” has been standardized by IEEE in the 802.11 series of specifications (i.e., as “IEEE Standard for Information technology—Telecommunications and information exchange between systems. Local and metropolitan area networks—Specific requirements. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”). As currently specified, Wi-Fi systems are primarily operated in the 2.4 GHz or 5 GHz bands.
Cellular operators that are currently serving mobile users with, for example, any of the technologies standardized by the 3rd-Generation Partnership Project (3GPP), including the radio-access technologies known as Long-Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS)/Wideband Code-Division Multiple Access (WCDMA), High Speed Packet Access (HSPA) and Global System for Mobile Communications (GSM), see Wi-Fi as a wireless technology that can provide good additional support for users in their regular cellular networks. There is interest around using the Wi-Fi technology as an extension, or alternative to cellular radio access network technologies to handle the always increasing wireless bandwidth demands. The term “operator-controlled Wi-Fi” points to a Wi-Fi deployment that on some level is integrated with a cellular network operator's existing network and where the 3GPP radio access networks and the Wi-Fi wireless access may even be connected to the same core network and provide the same services.
However, most current Wi-Fi/WLAN deployments are totally separate from mobile cellular communication networks, and can be seen as non-integrated from the terminal device's perspective. Most operating systems (OSs) for terminal devices such as Android™ and iOS®, support a simple Wi-Fi offloading mechanism where a user equipment, UE (the term used to refer to terminal devices by 3GPP) immediately switches all its Internet Protocol (IP) traffic or Packet-Switched (PS) bearers to a Wi-Fi network upon a detection of a suitable network with a received signal strength above a certain level. Henceforth, the decision to offload to a Wi-Fi or not is referred to as access network selection and/or traffic steering and the term “Wi-Fi-if-coverage” is used to refer to the aforementioned strategy of selecting Wi-Fi whenever such a network is detected.
There are several drawbacks of the “Wi-Fi-if-coverage” strategy, which has led to intense activity in the area of operator-controlled Wi-Fi in several standardization organizations. In 3GPP, activities to connect Wi-Fi access points to the 3GPP-specified core network are pursued, and in Wi-Fi alliance, WFA, activities related to certification of Wi-Fi products are undertaken, which to some extent also is driven from the need to make Wi-Fi a viable wireless technology for cellular operators to support high bandwidth offerings in their networks. The term Wi-Fi offload is commonly used and points towards that cellular network operators seek means to offload traffic from their cellular networks to Wi-Fi, e.g., in peak-traffic-hours and in situations when the cellular network for one reason or another needs to be off-loaded, e.g., to provide requested quality of service, maximize bandwidth or simply for coverage.
Furthermore, 3GPP has agreed to specify a feature/mechanism for WLAN/3GPP Radio interworking which improves operator control with respect to how a UE performs access selection and/or traffic steering between 3GPP and WLANs belonging to the operator or its partners (it may even be so that the mechanism can be used for other, non-operator, WLANs as well, even though this is not the main target), and it is expected that the mechanism will be included in Release 12 of the 3GPP specifications for LTE.
In the mechanism, parameters and/or rules are evaluated for one or both of the 3GPP network and WLAN to determine if a terminal device that is currently using the 3GPP network should access and/or steer traffic to the WLAN and vice versa. According to the mechanism the parameters and/or rules must be satisfied for a certain time period before the terminal device accesses and/or steers traffic to a different network. The certain time period is monitored using a timer which is started when the parameters and/or rules are first satisfied. This timer is also referred to herein as a time-to-trigger timer, since it indicates for how long the parameters and/or rules have to be satisfied before the change in access network or traffic steering is triggered. One reason for the use of the timer is to avoid a terminal device from ‘ping-ponging’ between the 3GPP network and WLAN.